Currently there are a variety of in vitro screening assays used to test environmental compounds and potential drugs for mutagenic and carcinogenic activity. However these assays generally do not detect tumor promoters, thus economical screens for these agents are urgently needed. This application proposes to develop and test a novel, inexpensive in vitro screening assay to test large numbers of environmental compounds and drugs for tumor promoting activity. This assay is based on the new finding that many or all tumor promoters can inhibit or induce cellular resistance to the physiological process of cell death through apoptosis. The assay, termed, ApoScreen, will be validated by testing a panel of known promoters and non-promoting agents to determine if their effects on apoptosis correlate with previously published results in animal models of tumor promotion. The human U937 tumor cell line will be treated with each test agent using a high dose acute exposure or a low physiological dose chronic exposure protocol. Apoptosis in response to tumor necrosis factor or UV light will be assessed by measuring DNA fragmentation in an assay requiring only 2-3 hr. incubation. if ApoScreen shows good predictive ability, it will ultimately be used in conjunction with other surrogate assays to screen large numbers of compounds for those exhibiting tumor promoter characteristics. The most suspicious compounds can then be tested in the more expensive and time consuming animal models of tumor promotion. This approach should provide an efficient and economical mechanism to identify potentially dangerous compounds and reduce human exposure to tumor promoting agents.